In a mobile station communication system of CDMA, there is a problem in which since signals of a plurality of users are transmitted in the same band, reception quality deteriorates as a result of undergoing influence of interference signals.
An array antenna is known as an apparatus for eliminating the interference. The array antenna is an antenna that is capable of setting reception directivity freely to intensively receive only a desired signal by providing adjustment of each of amplitude and phase to a signal received by each antenna element after multiplying the received signal by weighting factor (hereinafter referred to as “reception weight”).
Moreover, as another apparatus for canceling interference, there is an interference signal canceling apparatus that cancels signals (interference) transmitted from users other than a desired user from received signals so as to extract a desired signal.
Then, it can be expected that the use of combination of the array antenna and the interference canceling apparatus provide a larger interference cancellation effect than each independent use.
However, when the array antenna and the interference signal canceling apparatus are simply combined, the interference signal canceling apparatus must be individually provided every channel corresponding to each user, and this increases the amount of calculations and the apparatus scale, so that some contrivance is required to be provided.
Conventionally, there is disclosed an interference canceling apparatus, which is combined with the a array antenna and which aims to reduce the amount of calculations and the apparatus scale in Unexamined Japanese Patent Publication HEI 11-205286 and the like.
An explanation will be given of the conventional interference canceling apparatus, which is combined with the array antenna, using a block diagram of FIG. 1. The explanation set forth below refers to a case on the assumption that the number of stages of the interference canceling apparatuses is 3, the number of users is 3, and the number of multipath is 3.
Moreover, since the first stage and second stage have the same configuration as illustrated in FIG. 1, the explanation of the second stage is omitted.
In FIG. 1, antennas 11-1 and 11-2 form an array antenna, and a signal (hereinafter referred to as “first received signal”) received by the antenna 11-1 is inputted to ICUs (Interference Canceling Units) 12-1 to 12-3 and a delayer 13-1. Similarly, a signal (herainafter referred to as “second received signal”) received by the antenna 11-2 is inputted to ICUs (Interference Canceling Units) 12-1 to 12-3 and a delayer 13-2.
ICUs 12-1 to 12-3 are provided to correspond to users 1 to 3, respectively, to generate replica signals in connection with the first received signal and the second received signal (hereinafter referred to as “first replica signal” and “second replica signal”, respectively). The first replica signals generated by ICUs 12-1 to 12-3 are inputted to adders 14-1 and 15-1 and the second replica signal generated by ICUs 12-1 to 12-3 are inputted to adders 14-2 and 15-2. The configuration of ICUs 12-1 to 12-3 will be described later.
The delayers 13-1 and 13-2 delay the received signals by the processing time of ICUB 12-1 to 12-3, and each outputs the resultant to each of the adders 14-1 and 14-2.
At the adder 14-1, the first replica signal of each of the respective users 1 to 3 is subtracted from the first signal. Also, the second replica signal of each of the respective users 1 to 3 is subtracted from the second signal. This cancels all replica signals of all users from the received signals of the respective antennas. The output signals of adders 14-1 and 14-2 from which the replica signals of all users are canceled from the received signals are referred to as a first residual signal and a second residual signal, respectively. The first residual signal and the second residual signal are inputted to adders 15-1 and 15-2 and the delayers 13-1 and 13-2 of the second stage.
The adder 15-1 adds the first replica signal and the first residual signal on a user-by-user basis. Similarly, the adder 15-2 adds the second replica signal and the second residual signal on a user-by-user basis. This cancels the interference signal from the received signal on an antenna-by-antenna basis so as to obtain a desired signal. Namely, for example, when attention is paid to user 1, the signal of user 2 and the signal of user 3, which cause interference with user 1, are eliminated from the received signal to obtain a desired signal about user 1 for every antenna. The same is applied to the signal of user 2 and the signal of user 3. The obtained desired signals are inputted to ICUs 12-1 to 12-3 of the second stage, respectively.
According to the conventional interference signal canceling apparatus, the same processing as performed in the first stage is repeated in the second stage, so that the accuracy of replica signal is improved and that of the interference signal cancellation is improved. In other words, the more the number of stages are increased, the more the interference signals about the respective users sent from the other users are canceled.
The output signals of the adders 15-1 and 15-2 of the second stage are demodulated by the ICUs 16-1 to 16-3. This obtains demodulated signals 1 to 3 of the users 1 to 3. The configuration of each of the ICUs 16-1 to 16-3 will be described later.
An explanation will be next given of ICUs 12-1 to 12-3 and ICUs 16-1 to 16-3. In this case, ICUs 12-1 to 12-3 of the first and second stages have the same configuration and operation, respectively. Also, ICUs 16-1 to 16-3 of the third stage have the same configuration and operation. Accordingly, in the explanation set forth below, the ICU 12-1 of the first stage corresponding to the user 1 and the ICU 16-1 of the third stage are explained, and the explanation of the respective ICUs corresponding to the user 2 and the user 3 is omitted.
FIG. 2 is a block diagram illustrating a schematic configuration of ICU 12-1 illustrated in FIG. 1, and FIG. 3 is a block diagram illustrating a schematic configuration of ICU 16-1 illustrated in FIG. 1.
In FIG. 2 and FIG. 3, it is assumed that the number of multipath to the radio receiving apparatus is 3 and that the respective configuration parts for the respective paths are shown by P1 to P3, respectively. Since the respective configuration parts for the respective paths have the same configuration and operation, only the first path P1 is explained, and the explanation of the second path P2 and third path P3 is omitted.
In FIG. 2, the ICU 12-1 is divided into a front stage S1 where the signals received by the respective antennas 11-1 and 11-2 are subjected to despreading and then the resultants are multiplied by reception weights of the receptive antennas, respectively; a middle stage S2 where RAKE combining and temporary determination are carried out; and a back stage S3 where the signal, subjected to temporary determination, is multiplied by a replica weight to perform re-spreading so as to generate a replica signal.
The first signal received by the antenna 11-1 is inputted to a despreader 21-1 and the second signal received by antenna 11-2 is inputted to a despreader 21-2. The despreader 21-1 provides despreading to the first received signal to generate a despread signal X1. Similarly, the despreader 21-2 provides despreading to the second received signal to generate a despread signal X2. Despread signals X1 and X2 are inputted to multipliers 22-1, 22-2, and a reception weight calculator 23.
The reception weight calculator 23 calculates weights W1 and W2 of each antenna, and outputs the resultants to multipliers 22-1 and 22-1, and a complex conjugate calculator 30-1 and 30-2.
The multipliers 22-1 and 22-2 multiply despread signals X1 and X2 by reception weights W1 and W2, respectively, and an adder 24 adds the output signal of the multiplier 22-1 and the output signal of the multiplier 22-2 to carry out array combining. The signal subjected to array combining is outputted to a channel estimator 25 and a multiplier 26.
The channel estimator 25 performs the channel estimation based on the signal subjected to the array combining, and outputs the resultant to a complex conjugate ha* of a channel estimation value ha to the multiplier 26, and outputs the channel estimation value ha to a multiplier 29. The multiplier 26 multiplies the signal subjected to the array combining by the complex conjugate ha* of the channel estimation value. This compensates for phase rotation of the signal subjected to the array combining. The output signal of the multiplier 26 of each of paths P1 to P3 is inputted to a RAKE combiner 27 of the middle stage S2.
The RAKE combiner 27 provides RAKE combining to the signals of the respective paths P1 to P3 subjected to array combining, and a determining device 28 performs temporary determination to the RAKE combined signal outputted from the RAKE combiner 27. A signal d, which has been subjected to temporary determination and output from the determining device 28, is inputted to the multiplier 29 of the back stage S3.
The multiplier 29 of the back stage S3 multiplies the signal d subjected to temporary determination by the channel estimation value ha for each of paths P1 to P3, and the resultants are inputted to multipliers 31-1 and 31-2, respectively.
The complex conjugate calculator 30-1 and 30-2 calculate the complex conjugates W1* and W2* of reception weights and outputs the resultants to the multipliers 31-1 and 31-2, respectively.
The multipliers 31-1 and 31-2 multiply the output signals of the multiplier 29 by the complex conjugates W1* and W2* of reception, respectively. This obtains replica signals Xr1 and XR2 corresponding to X1 and X2 respectively.
A re-spreader 32-1 spreads the replica signal Xr1 and outputs the resultant to an adder 33-1. Similarly, a re-spreader 32-2 spreads the replica signal Xr2 and outputs the resultant to an adder 33-2.
The adder 33-1 adds the replica signal Xr1, which has been re-spread for each of paths P1 to P3, to generate a first replica signal and outputs the first replica signal to an adder 15-1. Similarly, The adder 33-2 adds the replica signal Xr2, which has been re-spread for each of paths P1 to P3, to generate a second replica signal and outputs the second replica signal to an adder 15-2.
Next, the ICU 16-1 of the third stage will be described. As illustrated in FIG. 3, the ICU 16-1 of the third stage has substantially the same configuration as that of the front stage S1 of the ICU 12-1 and that of the middle stage S2. Accordingly, the same reference numerals are added to the same configuration parts as those of the ICU 12-1 of FIG. 2, and the explanation of the ICU 16-1 of the third stage will be omitted.
The output signal of the determining device 28 of the ICU 16-1 is outputted to an external apparatus (not shown) as a demodulation signal.
In this way, the conventional signal canceling apparatus generates the replica signal for every antenna that forms the array antenna so as to improve the reduction in the amount of calculations and the circuit scale.
However, it is assumed that the number of users is L, the number of antennas is K, and the number of paths is M. Since it is necessary to provide (L×K×M) reception weight multipliers and (L×M) reception weight calculators to the conventional signal canceling apparatus as an entirety of apparatus, further reduction in the amount of calculations and the circuit scale is required.